Cancer is a major public health problem in the United States and other parts of the world. Currently, 1 in 4 deaths in the United States is due to cancer. Angiogenesis plays a critical role in tumor growth and metastasis in most types of cancer. In particular, its importance has been demonstrated in breast cancer, the most commonly diagnosed female malignancy in the United States. Anti-angiogenic therapeutics, either as a monotherapy or in combination with other therapeutics, are promising and are being intensely investigated in both preclinical and clinical studies. Anti-VEGF therapeutics showed early promise in clinical trials; however, although an anti-VEGF antibody bevacizumab (Genentech/Roche) was approved by the Food and Drug Administration (FDA) for breast cancer in 2008 in combination with chemotherapy, in November 2011, the FDA revoked the breast cancer indication because it has not demonstrated an overall survival benefit.
The development of anti-angiogenic therapies to treat breast and other cancers, as well as, ocular proliferative diseases, such as age-related macular degeneration, is ongoing. Lymphangiogenesis also plays an important role in cancer metastasis (Holopainen et al., 2011). To date, no peptide drugs have been approved for the treatment of cancer or other angiogenesis- and lymphangiogenesis-dependent diseases.
Peptides have been employed as therapeutics for multiple diseases and recently have been investigated in clinical applications to target tumors either for imaging or therapy (Folkman, 2010; Senger et al., 1983; Leung et al., 1989; Carmeliet, 2005; Carmeliet and Jain, 2000; Carmeliet and Jain, 2011; Rosca et al., 2011). Mimetic peptides are peptides that biologically mimic active determinants on biomolecules. In general, peptides are attractive tools as therapeutics due to their specific target binding, ability to penetrate cells and ease of modification giving flexibility for different applications (Carmeliet and Jain, 2000; Folkman, 2006). In addition, they are less toxic because they bind to their targets with high specificity and they are inexpensive to produce.
Some of the properties that make peptides attractive candidates, however, also contribute to their disadvantages. Although peptides can interact specifically with cellular receptors, sometimes these interactions may be of low affinity. In addition, the use of peptides as therapeutic agents is currently limited due to their short half-life and reduced bioavailability. Attempts to modify a peptide to increase its bioavailability include substitution with non-natural amino acids, pegylation of the peptide, and delivery of the peptide in a nano- or micro-particle.